Throughout the years, there has been a desire to alter the color of synthetic and natural fibers. In particular, coloring of human hair has been sought in view of changing styles and fashion.
The coloring of hair is currently subject to the most varied trends. Whereas in the past hair was colored primarily to cover gray hair, today there is an increasing demand for integrating the hair color into current fashion as an expression of personality.
Now as before, two established methods of hair coloring are broadly applied. One is the semi-permanent system which consists of the possibility of coloring hair with colorants containing non-oxidative, direct dyes (often referred to as toners). Although the dyes used for this purpose are optimized for dyeing performance as well as for remaining on the hair as long as possible, the color shade gradually weakens with every hair washing Thus, depending on the type of hair and the used product, such colorants as a rule do not last more than a maximum of 10 hair washings. Although designed for direct dyeing, some of these dyes can also be applied in presence of hydrogen peroxide in order to intensify the color result and to obtain better root-to-tip evenness.
Besides the semi-permanent system, oxidation dyes have attained substantial cosmetic significance in the field of conventional hair dyeing. The color is created by reaction of certain primary intermediates and couplers in the presence of an oxidant. In addition to the creation of color effects, very high requirements are placed on oxidation dyes that are intended for the treatment of human hair. On the one hand, the dyes must be safe from a toxicological and dermatological point of view. Moreover, it must be possible, by a combination of suitable primary intermediates and couplers, to produce a wide range of different color nuances. Furthermore, the hair colorations produced are required to have good wash fastness, light fastness, perspiration resistance, resistance to permanent wave treatments, acid resistance, base resistance and abrasion resistance. At any rate, such hair colorations must remain stable for at least four to six weeks under normal everyday conditions.
The oxidative system is based on the reaction of so called primary intermediates with couplers; both molecule types are practically colorless. In presence of air or oxidants such as hydrogen peroxide, primary aromatic amines with an additional hydroxy, amino, mono- or di-substituted amino groups in the para or ortho position react with couplers of the resorcinol, m-aminophenol, m-phenylenediamine or 1-naphthol type. Some years ago, a new primary intermediate, a substituted 4,5-diaminopyrazole, was introduced to provide intense red shades with most of the commonly used couplers.
As the size of the dye molecules formed in the hair is larger than the size of the highly diffusible starting primary intermediates and couplers, no significant fading normally occurs after dyeing. Therefore the oxidative hair coloring which produces a very durable coloring result is also called “permanent” system.
The base used for pH adjustment has preferably been ammonium hydroxide. The advantage of using ammonium hydroxide is that the combination with hydrogen peroxide provides slight enlightening of the hair. During processing, enlightening occurs in parallel with coloring the hair. In this connection, the lightening effect is essential for providing even color results.
A number of primary hydroxyalkylamines which are mostly odorless can be used instead of ammonium hydroxide, which has a characteristic pungent odor. As alkanolamines are not volatile under hair coloring conditions the hair has to be well rinsed after processing.
Over the years, classes for hair colorants have been established. Hair colorants based on cream or gel are very common in European countries. Liquid formulations which, when mixed with aqueous hydrogen peroxide compositions, form a gel are preferred in numerous American countries. The colorants can either be prepared and applied by the traditional way; in particular hairdressers prepare the ready-to-use mixtures in a bowl and apply it by a brush; or compositions are shakable and are therefore preferentially mixed with the developer composition in a vessel. Then the colorants are applied from the vessel via a nozzle or a system of nozzles which have the design of a comb. The latter is especially suitable for applications at home. In all these cases it is ensured that the hair colorants remain exactly where applied and do not drip from the head during time application.
The gel base for oxidation dyes should be the choice when the hairdresser wants a transparent texture that is easy to mix with hydrogen peroxide, changing itself into a cream appearance upon mixing or, in some cases, with transparent peroxide, maintains the transparence of mixture. A first example of gel in oxidation tint was disclosed in FR1311807.
Despite considerable advantages in terms of aesthetic appearance and easiness to mix, the gel can also have significant inconveniences.
Depending on the individual condition of the hair which can be from non-damaged to damaged, from dry to greasy, from thin to thick, from short to long, the composition on-head may not always have the required stability over the whole processing time. Especially at extended processing times, compositions have a tendency to run down from the head so an important amount of composition cannot be retained by the hair with reduced efficacy of the treatment.
There is still a need for agents that can impart uniform coloration with high intensity and vividness as well as a good gray coverage capability is a continuous focus of development. Finally current hair dyes, due to the plurality of ingredients, have shown to frequently possess unsatisfactory rheological properties. These are particularly evident from the viscosity variation during shelf life. For example, agents that thicken during storage are associated with issues such as lose of viscosity stability, dosing and application. Another need is to increase tackiness to the hair fiber and manageability during application with bowl and brush.
Consequently, an object of the invention is to mitigate the above mentioned disadvantages of oxidative gel hair dyes by improving rheological properties, viscosity stability and manageability during application with bowl and brush, tackiness to the hair, brightness and evenness from growth to the tips.